1. Field of the Invention
The present invention relates to spinal fixation systems for use in the treatment of spinal deformities and more particularly to a clamping connector for attaching angularly misaligned pedicle screws to transverse spinal rods in spinal fixation systems.
2. Description of the Prior Art
Surgeons treat spinal disorders with spinal fusion augmented with longitudinal spinal rods connected to the spine with lamina hooks or pedicle screws. Such xe2x80x9crod assembliesxe2x80x9d generally comprise one or two spinal rods and a plurality of screws inserted through the pedicles and into their respective vertebral bodies. The screws are provided with coupling elements, for coupling the elongate rod to the screws. The rods extends along the longitudinal axis of the spine, coupling to the plurality of screws via their coupling elements. The aligning influence of the rod forces the spine to which it is affixed, to conform to a more proper shape.
Due to anatomical variations, pedicle screws may not properly align with the longitudinal spinal rods. In order to eliminate the need for lateral rod bending, a device is required to connect the rod to the screws in such a way as to compensate for lateral deviation of the spinal rods.
The art contains a variety of attempts at providing instrumentation that permits a range freedom with respect to angulation of the screw and the coupling element. These teachings, however, have generally been complex, and unreliable with respect to durability. The considerable drawbacks associated with the prior art systems include complexity, difficulty properly positioning the rod and the coupling elements, and the tedious manipulation of many small parts associated with the complex spinal fixation devices.
Various connector designs exists to accommodate screws offset from the rod, these include the Smith and Nephew Rogozinski (U.S. Pat. No. 5,102,412) and Finn Systems (U.S. Pat. No. 5,474,551), the Synthes Universal System, and the Zimmer Modulok System (now the Wrightlok System from Wright Medical). Each of these systems require two locking mechanisms for the connectorxe2x80x94one to link the pedicle screw to the connector and another to link the connector to the rod. Some of these devices provide variable lateral adjustment while other provide only a fixed distance of offset. The Sofmor Danek TSRH System (U.S. Pat No. 5,282,801) provides a means to offset a screw from the rod with a single set screw yet the lateral distances are fixed.
Other types of screws, hooks and clamps have been used for attaching corrective spinal instrumentation to selected portions of the patient""s spine. Examples of pedicle screws and other types of attachments are shown in U.S. Pat. Nos. 5,562,662, 5,498,262, 5,312,404, 5,209,752 and 5,002,542. However, many current bolt to rod connectors constrain the bolt or screw to a predetermined angle in relation to the connector when the assembly is tightened. Tightening the bolt or screw to the connector forces the bolt or screw into a position perpendicular to the connector, creating stresses on the connector and on the bone as the bolt or screw is forced into the perpendicular position.
When spinal rod system are implanted in the sacral region of the spine, the bone screws need to allow for the variability in angulation found between the sacral and lumbar vertebrae. The bone screws also need to be able to pivot in the medial/lateral plane as well as have the ability to pivot and lock in the cephalad/caudal plane while maintaining the proper alignment between an implanted bone screw, a coupler and a rod of a spinal fixation system.
Accordingly, it is a principal object of the present invention to provide a spinal rod linkage apparatus for connecting two or more vertebral bodies in a lateral direction whereby healing of a bone graft between the vertebral bodies is enhanced.
It is another object of the present invention to provide a connector that compensates for angular misalignment, in the transverse plane between both the implanted bolt or screw and the spinal rod, and the bolt or screw and the connector in order to reduce stress on the bolt or screw when it is firmly fastened to the connector.
It is a further object of the present invention to provide a connector that allows for attachment to both the spinal rod and the implanted bone screw with only one locking mechanism.
It is another object of the present invention to provide a connector that provides for variable lateral distances between the spinal rod and the implanted pedicle screw.
The present invention is directed to a one piece connector for connecting angularly misaligned implanted pedicle screws to longitudinal spinal rods in spinal fixation systems. The one piece connector has a body portion and a leg portion that intersects the body portion at a 90xc2x0 angle. The body portion includes a bore having an inside diameter and a longitudinal axis, with the longitudinal axis of the bore being positioned perpendicular to the longitudinal axis of the leg portion. The leg portion includes a slot placed through a section of the leg portion, the slot being placed along the transverse axis of the leg portion and parallel to the longitudinal axis of the leg portion. The slot intersects the bore of the body portion perpendicular to the longitudinal axis of the bore. The slot allows the one piece connector to be securely clamped around a longitudinal spinal rod when a pedicle screw is implanted at variable distances from the longitudinal spinal rod. The one piece connector allows for angular misalignment of an implanted pedicle screw in relation to a longitudinal spinal rod and the one piece connector, and for the attachment of the one piece connector to both the longitudinal spinal rod and to the implanted pedicle screw with a single locking mechanism when the one piece connector is used in a spinal fixation system.